Copyright c 2001 The McGraw-Hill Companies, Inc.1 Chapter 8 Quantitative Research Designs

Copyright c 2001 The McGraw-Hill Companies, Inc.2 The Experimental Framework Used to determine causation Conducted in lab or other controlled setting To control for extraneous influences Independent variable is manipulated by researcher Participants randomly assigned to conditions or treatments

Copyright c 2001 The McGraw-Hill Companies, Inc.3 The Classical Experiment Researcher controls Selection of treatment & control groups – based on theory Random assignment of participants to conditions – ensures participants in each condition are equivalent before any treatment Manipulation checks

Copyright c 2001 The McGraw-Hill Companies, Inc.4 Posttest Experimental Design

Copyright c 2001 The McGraw-Hill Companies, Inc.5 Pretest-Posttest Experimental Design

Copyright c 2001 The McGraw-Hill Companies, Inc.6 Factorial Experimental Design Treatment groups based on two or more independent variables Dependent variable measured once after treatment given Can test for main and interaction effects

Copyright c 2001 The McGraw-Hill Companies, Inc.7 Longitudinal Experimental Designs Multiple measurements of the dependent variable Time between measurements depends on the nature of the communication phenomenon studied Used for studying training effects or degree of retention

Copyright c 2001 The McGraw-Hill Companies, Inc.8 Evaluating Experimental Design Strengths Researcher controls manipulation of IV Assumes that any effect on DV is the cause of the IV Precision Limitations Not all communication can be studied using experiments Other external influence may be the cause of DV change May not reflect reality

Copyright c 2001 The McGraw-Hill Companies, Inc.9 Quasi-Experiments Researcher relies on natural variation of independent variable Posttest, pretest-posttest, factorial, and longitudinal designs can be used Includes mock experiments, simulations, and field experiments

Copyright c 2001 The McGraw-Hill Companies, Inc.10 Non-experimental Designs Also called correlational or descriptive studies Researcher does not control manipulation of IV Participants not randomly assigned to conditions Predictor and criterion are better labels for IV and DV as they do not imply causality

Copyright c 2001 The McGraw-Hill Companies, Inc.11 Researcher Effects and Procedural Bias Introduced in interaction with participants Similarity of researcher to participants How researcher communicates to participants Researcher unknowingly encourages desired responses Demand characteristics created when topic has socially desirable elements Use research protocol to detail procedural steps

Copyright c 2001 The McGraw-Hill Companies, Inc.12 Comparing Research Designs